Question

A free electron is placed between two large, parallel,nonconducting
plates that are horizontal and 3.6 cm apart. One plate has a
uniform positivecharge; the other has an equal amount of uniform
negative charge.The force on the electron due to the electric field
betweenthe plates balances the gravitational force on the
electron.

(a) What is the magnitude of the surface charge density on
theplates?
C/m2